Alkaline detergents



Patented Dec. 1945 T; oi-"Flor:

' DETERGENTS Charles SEhwartz, Pittsburgh, Pa.

No Drawing. Application December 3, 1942,

7 Serial No. 467,793 7 W 6 Claims. (01. 252-99) This invention relates generally to alkaline detergents for cleaning tin, the detergent containing a combination of corrosion inhibiting agents.

It is a well known fact that many highly a1- kaline detergents, while performing excellently as cleaners, can not be used for cleaning tin, since the alkalies corrode and dissolve the tin quite readily.

My alkaline detergent composition is useful in all cases where a highly alkaline detergent is required. In the fabrication of tin plate or articles made therefrom, it is often necessary to apply grease in the forming operations. This may be removed by the use of a highly alkaline cleaning solution in accordance with the present invention without attack on the tin. The detergent l osition may be used in the washing of dairy equipment, milk cans and bakery pans.

I have found that detergent compositions containing large proportions of sodium metasilicate or other alkali-metal metasilicate such as potassium metasllicate may be used for cleaning tin while preventing corrosion thereof, provided that the sodium metasilicate contains certain combinations of inhibiting agents. It i essential that a combination of the inhibiting agents be used, because it has been found that none of them taken singly will efiectively inhibit the corrosion of tin. My detergent composition contains alkalimetal metasilicate as the principal alkaline ingredient. It may contain other ingredients but these other ingredients must not be more alkaline than the sodium metasilicate, if they are used in large amounts. For example, I might use, aay, up to 5% of sodium hydroxide in the composition and, although this is more alkaline than ;odium metasilicate, the relatively small amount )1. the sodium hydroxide would not greatly in- :rease the alkalinity of the detergent composiion. The detergent compositiomwhether it conains only alkali-metal metasilicate as the deersent or whether it contains a small amount of t more strongly alkaline detergent than the metailicate, always contains a combination of corosion inhibiting agents. One of these inhibiting gents is an alkali-metal perborate, for example odium perborate. Another of the inhibiting ents is a water-soluble salt of zinc, for examle zinc sulphate. The third inhibiting agent is water soluble salt of magnesium, for example magnesium sulphate, and/or an alkali-metal siliate having a low ratio of alkali-metal oxide to 10:. This low ratio alkali-metal silicate has ratio of M20 to 8102 of not over 1:2, wherein M :presents sodium or potassium. This "low rau of M20 to S102 of 1:1.

tio alkali-metal silicate is to be distinguished from the alkali-metal metasilicate having a ratio For purposes of simplicity, I shall refer hereinafter to low ratio alkali-metal silicate to designate thosealkalimetal silicates in which the ratio of alkali-metal oxide to SiOz is not over 1:2.

The low ratio sodium silicate may. therefore, be considered as an equivalent of a water-soluble magnesium salt, since either the low ratio sodium or potassium silicate or a water-soluble magnesium salt when used in combination with a water-soluble zinc salt and an alkali-metal perborate will inhibit the corrosion of tin by solutions of sodium metasilicate. The detergent composition always contains alkali-metal metasilicate as its principal alkaline ingredientand also contains an alkali perborate, a water-soluble salt of zinc and either or both a water-soluble salt of magnesium and a low ratio alkali-metal silicate.

Specific examples 01 my detergent composition are:

Example 1 Per cent Sodium metasilicatenu; 86 Sodium perborate -s 10 Zinc sulphate 2 Magnesium sulphate 2 Example 2 I Per cent Sodium metasilicate 83 Sodium perborate 10 Zinc sulphate 2 Low ratio sodium silicate 5 Each of these compositions has been tested to determine its corrosion effect on tin. A 1% aqueous solution of each detergent composition was made up and strips of tin were immersed in the solution for one hour while maintaining the solution at boiling temperature. The strips were weighed before and after immersion and the loss in weight determined. In using each of the two solutions, it was found that the loss in weight was 0.0 mg., the original tin strip weighing ap proximately 5 grams. These tests show that the combination of inhibiting agents eflectively inhibited the corrosion oi the tin.. As contrasted with the results of the tests obtained from Examples 1 and 2, it was found that in using a 1% solution 01' a detergent containing 90% sodium metasilicate and 10% sodium perborate the loss in weight under the same conditions was 6.9 to 7.9 m. r

about 70 to 90%.

While the combination of zinc sulphate and either magnesium sulphate or low ratio sodium silicate, when added to sodium metasilicate and sodium perborate, is effective in inhibiting corrosion of tin, I have found that no one of the Table I NEED; g

In my detergent composition, alkali-metal metasilicate, for example sodium or potassium metasilicate, constitutes the principal alkaline ingredientl It may amount to from 60 to 93% by weight of the composition but is preferably from The alkali-metal perborate constitutes about 3 to 20%, preferably from 5 to 15%, or more specifically from about '7 to 12% of the composition. The water-soluble salts of zinc and magnesium and the low ratio alkali-metal silicate are each used in amounts of at least about 1% and may constitute or even higher percentages of the composition. Preferably each is between about 2% and 7%. The total of the zinc salt and the magnesium salt or low ratio silicate is from about 2 to 10% or even higher but preferably between about 3% and 7%.

For washing bakery pans or milk cans, I may use either of the compositions given in Examples 1 and 2. The detergent composition is dissolved in water to form a solution of a strength between /4 of 1% and 3%, preferably a, 1% solution. The articles may be boiled in the cleaning solution for an hour, if need be, without corroding the tin.

Instead of zinc sulphate I may use any other water-soluble salt of zinc, since the action of inhibiting corrosion does not depend upon the particular zinc salt employed but depends upon the zinc metal of the inhibiting agent. I may, for example, use zinc chloride, zinc nitrate or zinc acetate. Similarly in place of themagnesium sulphate I may use magnesium acetate, magnesium chloride or magnesium nitrate. Likewise in place of the low ratio sodium silicate I may use the corresponding 10w ratio potassium silicate;

Other agents which aid in th cleaning operation, such as soap, casein, deflocculating agents, wetting agents, abrasives and the like, may be added to the detergent composition containing alkali-metal metasilicate, alkali-metal perborate, a water soluble zinc salt and either or both a water-soluble magnesium salt and low ratio a1- kali-metal silicate.

The present invention deals only with alkaline detergents which are to be used in cleaning tin. The combination of inhibiting agents of Examples 1 and 2 and shown by tests to inhibit the corrosion of tin have been tested in a similar manner in cleaning aluminum. It has been found that these detergent compositions, althougheffective in inhibiting corrosion of tin are not effective in inhibiting corrosion of aluminum.

The invention is not limited to the examples, which have been given merely fo illustrative purposes, or to the specific proportions but may be otherwise embodied or practiced within th scope of the following claims.

I claim:

1. An alkaline detergent composition for cleaning tin, comprising by weight about 60 to 93% alkali-metal metasilicate, about 3 to 20% alkalimetal perborate, about 1 to 10% of a water-soluble salt of zinc and about 1 to 10% of at least one inhibitor of the group consisting of a watersoluble salt of magnesium and an alkali-metal silicate having a ratio of M20 to SiOz of not over 1:2, wherein M represents a member of the group consisting of sodium and potassium.

2. Analkaline detergent composition for cleaning tin, comprising by weight about 60 to 93% sodium metasilicate, about 3 to 20% alkali-metal perborate, about 1 to 10% of a Water-soluble zinc salt and about 1 to 10% of a water-soluble magnesium salt.

3. An alkaline detergent composition for cleaning tin, comprising by weight about 60 to 93% sodium metasilicate, about 3 to 20% alkali-metal perborate, about 1 to 10% of a water-soluble zinc salt and about 1 to 10% of an alkali-metal silicate having a ratio of M20 to SiOz of not over 1:2, Where M represents a member of the group consisting of sodium and potassium.

4. An alkaline detergent composition for cleaning tin, comprising by weight about to sodium metasilicate, about 5 to 15% sodium perborate, about 2 to 7% of a Water-soluble zinc salt and about 2 to 7% of at least one inhibitor of the group consisting of a water-soluble salt of magnesium and an alkali-metal silicate having a ratio of M20 to SiOz of not over 1:2, wherein M represents a member of the group consisting of sodium and potassium.

5. An alkaline detergent composition for cleaning tin, comprising by weight about '70 to 90% sodium metasilicate, about 5 to 15% sodiumperborate, about '2 to 7% zinc sulphate and about 2 to 7% magnesium sulphate.

6. An alkaline detergent composition for cleaning tin, comprising by weight about '70 to 90% sodium metasilicate, about 5 to 15% sodium per-' borate, about 2 to 7% zinc sulphate and about 2 to 7% of odium silicate having a ratio of NazO to SiO2 of not over 1 :2. i

CHARLES SCHWARTZ. 

